The present invention relates to a device for measuring the position of a filament bundle in a spinning device for synthetic fibers.
In spinning frames for spinning synthetic fibers, the hot thread filaments leave the spinnerette in a bundle, and along a distance of roughly 2 to 6 meters a cooling means blows against the filaments. The filaments are withdrawn by a withdrawing means, are then twisted and wound onto a reel. The threads move at a rate of several m/sec. Since a stationary spinning condition should be achieved, an effort is made whenever possible, to measure the position and the variation of the center of gravity of the filament bundle at the location of the widest deflection of the bundle from the vertical. Heretofore, this has so far been done by the operators watching the process.
On pages 463 to 365 of the trade journal Melliand Textilberichte No. 7/1987, a system is disclosed which measures textile cloth by means of an optical system in order to detect the flaws and faults in the cloth. The system is not suitable, however, to measure the positions of filaments or of a filament bundle, since all of the light passing through the textile spot arrives in an integrating ball so as to be measured.
U.S. Pat. No. 3,659,950 discloses a system for measuring the position of a thread in which the light emitted by a laser is passed via deflector mirrors and directed onto the thread, whereupon it is received by a detector array system disposed directly in the optical path, before the image is analyzed. This system is also not unsuitable to measure the position of a bundle of filaments.
It is therefore the object of the present invention to provide a device which will permit the measurement of the position of a bundle of filaments so as to allow for the automatic detection of the position of the filament bundle.
This object is achieved according to the invention by arrangement of the detector means at an angle relative to the illumination, so that direct light from the source of light does not impinge on the detector means. The angle corresponds therefore to a value of 10.degree. to 45.degree. approximately. This angular disposition is required in particular since the intensity of the signal issuing from the individual fibers is less than 1 .mu.Watt while the source of light may produce an output of some 150 watts, so that the ratio amounts to roughly 1:10.sup.8 to 1:1.sup.9. Observation on a dark ground is therefore required. The detector means may be a TV camera or a matrix of photodiodes, for instance, or even a position-sensitive photodiode (PSD). In any case, an optical system such as a convergent lens must be positioned ahead of these sensors.
The invention is the first to allow for imaging a section of the fiber bundle onto a sensor so as to provide for measurement of the positions of both the individual fibers or the center of gravity of the bundle. Since the fiber gauge is roughly 10 .mu.m, there is no vignetting of individual filaments so that the individual positions or the center of gravity may actually be measured. The deflection from the vertical or the longitudinal axis of the thread amounts to several centimeters up to 20 cm, depending on the power of the blower and its distance from the spinnerette.
According to one embodiment of the invention, the light diffracted at the filaments is measured. The additional measurement of the intensity of the light impinging onto the sensor, allows for a measurement of the number of gauge or the filaments, respectively.
The angle enclosed between the illuminating means and the detector means moreover allows for the additional measurement of the position(s) in the illuminating direction, since variations in the position in the illuminating direction can be detected on the basis of the image in the form of variations of the height of the image on a two-dimensional sensor.
It is moreover expedient to operate the source of light in a pulsed mode or to pass the light intermittently through a suitable light valve. This is an advantageous provision since in such a case the light emitted from the environment may be filtered out, in a manner known per se, in an electronic unit.
When a CCD array is selected for the sensor, the width of the bundle may be calculated on the basis of the individual filament positions detected. When a PSD element is used, a further resolution of the individual positions is no longer possible. In such a case the width of the bundle may be measured then by means of a filter or, in an equivalent manner, by means of a modified illumination system. The principle of measurement is based on the measurement of the mean value of the position and on the additional measurement of a value such as the root mean square. This allows for the detection of the variance of the filament position in the blowing direction as the basis of calculation of the width of the bundle.
When the position of the filament bundle is measured by means of a two-dimensional analog position-sensitive sensor (PSD) in the x' direction, the mean value f(x') in the y' direction may be measured. The two measured mean values permit the derivation of the width of the bundle.
Furthermore, the positional variance is obtained from the mean values of x'.sup.2 and x', and thus the standard positional deflection of the image on the detector is determined as a basis for the calculation of the width of the bundle.
Instead of a single filter, it is possible to dispose, ahead of the sensor, a filter which consists of a plurality of polarizing filters. It is possible in this way to measure additionally the degree of polarization of the light diffracted at the filaments.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.